View of STUDY & OBSERVATION OF FLAT SLAB DESIGNED WITH HIDDEN BEAMS

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ACCENT JOURNAL OF ECONOMICS ECOLOGY & ENGINEERING

Peer Reviewed and Refereed Journal ISSN No. 2456-1037 IMPACT FACTOR: 7.98 (INTERNATIONAL JOURNAL) Vol. 05, Issue 10,October 2020 Available Online: www.ajeee.co.in/index.php/AJEEE

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STUDY & OBSERVATION OF FLAT SLAB DESIGNED WITH HIDDEN BEAMS Anurag Shrikhande

P.G. Student, Shri Ram Group of Institutions, Jabalpur, M.P., India Prof. Thakur Charan Singh

H.O.D., Civil Dept., Shri Ram Group of Institutions, Jabalpur, M.P., India Prof. Anil Kumar Sanodiya

Shri Ram Group of Institutions, Jabalpur, M.P., India

Abstract- In urban areas, multi storey buildings are the only solution for the increasing demand of lands. Due to increased architectural beautification, lesser number of columns are designed in the building, leading to longer span of beams. Due to structural design constraints depth of beam needs to be kept higher, which hinders the clear height of the room. One of the many solutions to steer clear of this problem is providing flat slab with drop or column head or both. This paper conducts a thorough analysis and design of flat slab without drops and column heads by using hidden beams. On the basis of results obtained, cross beams at column junctions proved to be more efficient, resulting in 23.07%

deflection control.

1 INTRODUCTION

A structure in which all the loads coming from the slab is taken by beam and column, and distributed to the subsoil by means of RCC footing is named as a framed structure. A Slab is a structural element of modern building, consisting a flat, horizontal/Inclined surface made of concrete and Reinforcement. Type of slabs

a. Beam-Slab Construction b. Flat Slab

c. Waffle Slab

To reduce the punching shear failure of slab and to control the excessive deflection in slab, it is recommended to provide flat slab either with drop panel or column head or by using both together. But providing a drop panel or column head do not look good aesthetically due to the increased depth.

This makes it necessary to provide a solution in design of flat slab by using different methodologies and control the excessive deflection of slab & Punching shear, without using the drop panel or column head.

Loading in various form (point load, uniformly distributed load, uniformly varying load) is applied on slabs which gets transfer to footing by beam & column action) .But these beams decreases the floor height resulting in lesser clear dimension inside the room. Flat slab proved to be a better solution which doesn't requires any beam, but contains drop or column head or both. In this paper, we moved one step further & focused on analysis and design of flat slab without head or drop.

2 ANALYSIS OF THE FLAT SLAB

The following 3 models were analyzed and designed using ETABS 2017 software CASE 1 Flat Slab without any Beam, drop and Column head CASE 2 Flat Slab with Hidden Beam in Cross (+) SHAP CASE 3 Flat Slab with Hidden Beam in Cross (X) way

All models are having same data for the parametric study. The data are listed in table below Span in X-Direction Span in Y-Direction

l1 =6.8 m , l2 =6.8 m l1 =6.8 m , l2 =6.8 m (i) Column strip (i) Column strip

= 0.25 l2 = 1.7 m = 0.25 l2 = 1.7 m

But not greater than 0.25 l1 = 1.7 m But not greater than 0.25 l1 = 1.7 m (ii) Middle strip (ii) Middle strip

= 6.8 – (1.7+1.7) = 3.4 m = 6.8 – (1.7+1.7) = 3.4 m

Overhang Slab= Column strip= 1.7 m Overhang Slab =Column strip=1.7 m Ln = clear span = 6.8-.8= 6m Ln = clear span = 6.8-.8= 6m

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Overall Slab length

Lx = 6.8+1.7+1.7 = 10.2 m Overall Slab length Ly = 6.8+1.7+1.7 = 10.2 m Column size (C1,C2,C3,C4) 800 mm X 800 mm

Thickness of Slab 210 mm

Live load 5 kN/m2

Floor finish 2 kN/m2

Factor Of Safety 1.5

Fig. 1 3 FLAT SLAB DESIGN STRIPS ARRANGEMENT

Flat slab analysis with hidden beams is somewhat an unnoticed area and limited research has been carried out so far. The study of this type of slab is therefore important to see its performance. The analysis and practical solutions regarding reduction in the sections of SLAB due to CROSS BEAM is interesting to observe. The efforts have been taken to perform the study of such type of SLABS from structural stability AND ASHTETIC CONDITIONS

Strip Moments Comparison between three Cases (By ETABS 2017) Case No. Deflection

(mm)

Column Strip Middle Strip REMARK -ve

Moment +ve

Moment -ve

Moment +ve Moment

Case 1 -18.882 - 333 + 196 - 20 + 175 Without any Beam, drop and Column head Case 2 -13.941 - 254 + 150 - 39 +140 With Hidden Beam in

Cross (+) SHAPE Case 3 -13.034 -204 + 150 - 39 + 138 With Hidden Beam in

Cross (X) SHAPE 4 FINAL CASE FOR TESTING

As per the results received from trial cases by ETABS software, Case no. 3 is found to be more efficient. Therefore this case is taken as final model. For comparative result in this Model, one part of Slab is taken with Cross Hidden Beam and other part is taken without any beam as shown in figure below. A prototype model of (1:10) is taken for experiment. 60 mm thick Raft is casted to support super structure, before commencing flat slab work.

Following specifications for slab was used for correlating results obtained by ETABS :- Grade of concrete M-25 (25 N/mm2)

Reinforcement fy-250(250 N/mm2)

Diameter of bars used 4 mm,2.5mm,2mm,1.63mm,1mm,.5mm

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Fig. 2 Final Testing Model 5 SCOPE AND ARRANGMENT

Scaled model was tested using “BAKER” company deflection sensor (dial gauge) having an accuracy of .01mm. 2 Nos. Dial Gauges were installed at a fixed position of 170 mm from the edge. The maximum (designed) load for the prototype is calculated below

Live load 5 kN/m2

Floor finishing 2 kN/m2

Total loading (factored@1.5) 10.5 kN/m2

Height of water required(for 1:10 model) 1.05 kN/m2/9.81 = 107 mm 6 TESTING OF SLAB

Fig. 3

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7 RESULTS AND CONCLUSION

PARTICULAR DEFLECTION AT G1 DEFLECTION AT G2

ETABS 210MM RCC SLAB -9.036 MM -11.942 MM

ETABS 21MM RCC SLAB -0.091 MM -0.120 MM

PROTOTYPE 21MM RCC SLAB -0.100 MM -0.130 MM

Percentage saving of deflection between both point of observation (with cross be am (G-1) &

without cross beam(G-2) ) = 23.07%

REFERENCES

1. IS: 875(part 1-5): “code of practice for structural safety of building loading standards”.

2. IS: 456-2000: “Code of practice for plain and reinforced concrete”.

3. “Advanced RCC Design” S.S. Bhavikatti.